Interhemispheric Integration of Letter Stimuli Presented Foveally or Extra-Foveally

Two experiments are reported in which participants decided whether a single target letter presented below and to the left or right of fixation matched either of two probe letters presented above the fixation cross to the left and right. The level of matching required was either physical (A-A) or abstract (A-a). All three letters were presented either extra-foveally (Experiment 1) or within the fovea (Experiment 2). In both experiments, physical matching was faster than abstract matching. Physical matching was faster within than across visual fields while abstract matching showed the opposite pattern. Matching was faster when the matching probe letter was in the LVF than when it was in the RVF. Importantly, the pattern of results was the same for extra-foveal and foveal presentations, supporting the theory that the representation of the fovea is split down the middle into two visual fields rather then being bilateral. The practical implication following this study is that lateralization studies can be performed with closer to fixation stimuli presentation.